The present invention relates to a control unit and a data transmitting method, and more particularly, an approach of communicating the data between a data recording apparatus and a control unit.
In the prior art, a data recording apparatus, for downloading a control parameter of a control unit mounted on the vehicle and recording the parameter in order to identify a faulty condition of the vehicle, is known. For example, JP-A-2002-070637 discloses a data recording apparatus for reliably and effectively recording the data of the control unit. In the data recording apparatus, various data in the control unit on the vehicle side are chronologically sampled and then the acquired sampling data are stored in the SRAM. Then, when the conditions under which the data that are useful for identifying the faulty condition of the vehicle will be obtained are satisfied, a series of sampling data stored in the SRAM are stored in the data recording section.
Meanwhile, since the control unit is prepared for the purpose of executing the control of the vehicle, the data recording apparatus must instruct the control unit to transmit the data in order to get the data of the control unit. Therefore, the data recording apparatus cannot acquire the data until such data recording apparatus instructs the control unit to transmit the data every time when the control unit is started in response to the start of the vehicle. From the viewpoint of improving the reliability of the recorded data, it is preferable that the data recording apparatus should record the data at the time of starting the vehicle, i.e., at the time of starting the control unit. However, since the control unit takes a time to some extent after it receives the instruction for data transmission and then prepares the transmitting condition to transmit the necessary data in response to this instruction, such a disadvantage arises that the control unit fails to record the data immediately after the starting.